Polyvinyl alcohol copolymer film for packaging liquid products and having an improved shelf-life

ABSTRACT

Generally speaking, the present invention is a water-soluble copolymer film comprising a hydrolyzed copolymer of vinyl acetate and a second monomer, the resultant polyvinyl alcohol copolymer having a degree of hydrolysis, expressed as a percentage of vinyl acetate units converted to vinyl alcohol units, of from about 90% to 100%. The second monomer is preferably selected from the group of monomers having carboxylate functionality or sulfonate functionality. The resulting water-soluble copolymer film is disclosed for use in making pouches to contain a unit dose of liquid detergent, such as a liquid laundry detergent. However, it is an aspect of the copolymer film that film solubility is not significantly affected adversely by the detergent. Such film produces pouches having a greater storage shelf-life over prior art water-soluble film.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 10/392,030 (now U.S.Pat. No. 7,022,656) filed Mar. 19, 2003 the disclosure of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to polyvinyl alcohol copolymerfilm for packaging liquid products, such as, for example, laundrydetergent. More specifically, the present invention relates to polyvinylalcohol copolymer film wherein the copolymer has structural featureswhich provide an improved film shelf-life.

BACKGROUND OF THE INVENTION

Polyvinyl alcohol (PVOH) is a synthetic resin generally prepared by thealcoholysis, usually termed hydrolysis or saponification, of polyvinylacetate. Fully hydrolyzed PVOH, where virtually all the acetate groupshave been converted to alcohol groups, is a strongly hydrogen-bonded,highly crystalline polymer which dissolves only in hot water—greaterthan about 140° F. (60° C.). If a sufficient number of acetate groupsare allowed to remain after the hydrolysis of polyvinyl acetate, thePVOH polymer then being known as partially hydrolyzed, it is more weaklyhydrogen-bonded and less crystalline and is soluble in cold water—lessthan about 50° F. (10° C.). Both fully and partially hydrolyzed PVOHtypes are commonly referred to as PVOH homopolymers although thepartially hydrolyzed type is technically a vinyl alcohol-vinyl acetatecopolymer.

The term PVOH copolymer is generally used to describe polymers that arederived by the hydrolysis of a copolymer of a vinyl ester, typicallyvinyl acetate, and another monomer. PVOH copolymers can be tailored todesired film characteristics by varying the kind and quantity ofcopolymerized monomers. Examples of copolymerizations are those of vinylacetate with a carboxylic acid or with an ester of a carboxylic acid.Again, if the hydrolysis of acetate groups in these copolymers is onlypartial, then the resulting polymer could be described as a PVOHterpolymer—having vinyl acetate, vinyl alcohol, and carboxylategroups—although it is commonly referred to as a copolymer.

It is known in the art that many PVOH copolymers, because of theirstructure, can be much more rapidly soluble in cold water than thepartially hydrolyzed type of PVOH homopolymers. Such copolymers havetherefore found considerable utility in the fabrication of packagingfilms for the unit dose presentation of various liquid and powderedproducts including agrochemicals, household and industrial cleaningchemicals, laundry detergents, water treatment chemicals and the like.

Examples of such copolymers are those prepared by the hydrolysis (basecatalyzed alcoholysis) of copolymers of vinyl acetate and carboxylicacid vinyl monomers, and copolymers of vinyl acetate and esters ofcarboxylic acid vinyl monomers. If sufficient base is present such thatthe acid groups (including those resulting from ester hydrolysis) areneutralized to form carboxylate salt groups i.e., ionomer groups, thecold water-solubility of these PVOH copolymers, and hence filmsfabricated from them, is very rapid. Examples of carboxylate-containingPVOH copolymers derived from monocarboxylic acid vinyl monomers andtheir esters are those prepared by the hydrolysis of a vinylacetate-acrylic acid copolymer, a vinyl acetate-crotonic acid copolymer,a vinyl acetate-methyl acrylate copolymer, a vinyl acetate-methacrylicacid copolymer, and a vinyl acetate-methyl methacrylate copolymer, allof which have excellent cold water-solubility. In fact, packaging filmsbased on PVOH copolymers having carboxylate groups are generallyconsidered in the art to be the most rapidly cold water-soluble films.

One of the largest markets for these films is the liquid laundrydetergent market where the convenience of the unit dose concept iswidely accepted and the rapid solubility of the films is particularlysuited to this application.

However, a significant problem exists with the chemical compatibility ofvirtually all liquid laundry detergent formulations and most of thecommercial film used to package these products. The commercial film isbased on a carboxylate-containing PVOH copolymer where the carboxylateunits, if converted to carboxylic acid groups, are readily able to formstable lactones by cyclizing with adjacent hydroxyl groups.Specifically, the chemical incompatibility derives from the acid-baseequilibria that exist in the liquid laundry detergent formulations andare usually in the form of amine-fatty acid equilibria and/oramine-anionic surfactant acid equilibria. Even if the detergentformulation is at an alkaline pH by virtue of the presence of a molarexcess of amine, exchangeable hydrogen ions are still available to reactwith the carboxylate groups of the PVOH copolymer. When this happens,carboxylic acid groups form and they in turn will readily react withadjacent hydroxyl groups to form intramolecular lactones if the lactoneshave stable five-membered (gamma, γ) ring structures. Other liquidproducts too numerous to mention may present similar chemicalincompatibilities and are, therefore, addressed by the presentinvention.

The solubility of the polymer and hence the film is markedly affected bythis reaction to form lactones; complete insolubility can occur in somecases resulting in polymer residues being attached to items of clothingat the end of a wash cycle. All the above-mentionedcarboxylate-containing copolymers derived from monocarboxylic acid vinylmonomers and their esters are subject to this reversion to stableγ-lactones in the presence of hydrogen ions. There is therefore a needto provide cold water-soluble films, preferably including those based onPVOH copolymers having carboxylate functionality (because of their fastsolubility) where the functional groups of the copolymers whichfacilitate cold water solubility are substantially unaffected byhydrogen ions or, if chemically modified by reaction with hydrogen ions,the modified functional groups do not significantly affect the watersolubility of the films.

SUMMARY OF THE INVENTION

A water-soluble copolymer film is disclosed for use in making pouches tocontain a liquid material, such as a liquid laundry detergent, whereinthe film solubility is not significantly affected adversely by thedetergent. Such film produces pouches having a greater storageshelf-life over prior art water-soluble film.

In one embodiment, the present water-soluble film comprises vinylacetate copolymerized with itaconic acid as a second monomer to produce,after hydrolysis, a polyvinyl alcohol copolymer with a degree ofhydrolysis, expressed as a percentage of vinyl acetate units convertedto vinyl alcohol units, from about 98% to about 100%.

In several other embodiments, the second monomer may be selected fromthe group of monomers consisting of monocarboxylic acid vinyl monomers,their esters and anhydrides, dicarboxylic monomers having apolymerizable double bond, their esters and anhydrides, and vinylsulfonic acid monomers and their alkali metal salts. The degree ofhydrolysis for these copolymer embodiments varies.

In such embodiments where the second monomer is one of eithermonocarboxylic acid vinyl monomers, their esters and anhydrides,dicarboxylic monomers having a polymerizable double bond, or theiresters and anhydrides, it is an aspect of the invention that the monomerbe specifically selected from the group consisting of vinyl acetic acid,maleic acid, monomethyl maleate, dimethyl maleate, maleic anhydride,itaconic acid, monomethyl itaconate, dimethyl itaconate, and itaconicanhydride. Most preferably, the second monomer is itaconic acid.

In other such embodiments it is an aspect of the invention that thesecond monomer is a vinyl sulfonic acid monomer or its alkali metalsalts. Specifically, the second monomer is selected from the group ofsulfonic acid monomers and their alkali metal salts consisting of vinylsulfonic acid, allyl sulfonic acid, ethylene sulfonic acid,2-acrylamido-1-methylpropanesulfonic acid,2-acrylamido-2-methylpropanesulfonic acid,2-methylacrylamido-2-methylpropanesulfonic acid, and 2-sulfoethylacrylate. Most preferably, the second monomer for these embodiments is2-acrylamido-2-methylpropanesulfonic acid.

Generally speaking, the present invention is a water-soluble copolymerfilm comprising vinyl acetate copolymerized with a second monomer toproduce a polyvinyl alcohol copolymer having certain structural featureswhich serve to improve the shelf life of the film, and wherein thesecond monomer is selected from the group consisting of monomers havingcarboxylate functionality or sulfonate functionality.

It is another aspect of the disclosed invention to produce a liquidproduct packet comprising a water-soluble film comprised of a polyvinylalcohol copolymer wherein a comonomer of the film copolymer is selectedfrom the group consisting of monocarboxylic acid vinyl monomers, theiresters and anhydrides, dicarboxylic monomers having a polymerizabledouble bond, their esters and anhydrides or vinyl sulfonic acid monomersand their alkali metal salts. The present embodiment includes a quantityof a liquid product enclosed within the water-soluble film packet.

These and other objects of the invention are disclosed and claimed inthe following detailed description of the invention, including theappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention described herein can be more readily understoodwith reference to the appended drawing figures where:

FIG. 1 is a perspective view of a test apparatus used to determine thewater disintegration and dissolution times of film samples;

FIG. 2 is a perspective view of the test apparatus and test set-upillustrating the procedure for determining the water-solubility of filmsamples; and

FIG. 3 is a top view of the test set-up of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible of embodiment in many differentforms, this disclosure will describe in detail preferred embodiments ofthe invention with the understanding that the present disclosure is tobe considered as an exemplification of the principles of the inventionand is not intended to limit the broad aspect of the invention to theembodiments illustrated.

In the present invention, specific monomers within three generalchemical classes are selected for copolymerization with vinyl acetatesuch that the base-catalyzed alcoholysis products of these copolymers,which are used in the formulation of the water-soluble film, retainexcellent solubility performance in the presence of hydrogen ions. Thecopolymers used in the formulation of the water-soluble films have oneof either 1) carboxylate functionality or 2) sulfonate functionality.

1. Copolymers with Carboxylate Functionality

Specific monocarboxylic acid vinyl monomers (for example, structure (a)shown below) and their esters and anhydrides, and specific dicarboxylicmonomers (for example, structure (b) shown below) having a polymerizabledouble bond and their esters and anhydrides are selected forcopolymerization with vinyl acetate.

The base-catalyzed alcoholysis products of these copolymers, which areused in the formulation of the water-soluble film, retain carboxylatefunctionality in the presence of hydrogen ions because of the low stericstability, and therefore non-formation, of six-membered (delta, δ)lactone rings. Examples of the selected monomers are vinyl acetic acid,maleic acid, monomethyl maleate, dimethyl maleate, maleic anhydride,itaconic acid, monomethyl itaconate, dimethyl itaconate and itaconicanhydride.

By way of illustration and comparison, structures (c) and (d) areprovided to show the sterically favored γ-lactone and the non-favoredδ-lactone, respectively, as they would form on the polyvinyl alcoholpolymer backbone:

A carboxylate-containing PVOH copolymer based on the copolymerizationof, for example, acrylic acid with vinyl acetate would have itscarboxylate unit directly attached to the polymer backbone andtherefore, when in the acid form, able to form a stable five-memberedγ-lactone (structure (c) above) by cyclizing with an adjacent hydroxylgroup. In contrast, a copolymer derived from vinyl acetic acid wouldhave a methylene group between the polymer backbone and the carboxylateunit; in this case, only a six-membered δ-lactone (structure (d) above)could form and this is not a sterically favorable entity. In the case ofothers such as itaconic acid, a dicarboxylic acid, one of thecarboxylate groups can ultimately form a γ-lactone but the other canonly form a δ-lactone; the latter therefore remains intact and filmsolubility is preserved.

In the present invention, the preferred monomer for copolymerizationwith vinyl acetate from the group of monomers providing carboxylatefunctionality is itaconic acid. The preferred water-soluble film istherefore based on a vinyl alcohol-co-itaconic acid (sodium salt)copolymer.

Copolymer Synthesis

The vinyl acetate-co-itaconic acid copolymer is prepared under nitrogen,and in methanol as solvent, using 2,2′-azobis(isobutyronitrile) (AIDBN)as initiator. Alcoholysis of this copolymer is carried out in methanolicsodium hydroxide and the recovered vinyl alcohol-co-itaconic acid(sodium salt) copolymer is ground, washed to remove residual sodiumacetate, and dried. These reactions are known in the art and have beenreported, for example, by Moritani et. al (Polymer Preprints, Japan, 31,126 (1982)).

The preferred degree of polymerization of the vinyl alcohol-co-itaconicacid (sodium salt) copolymer is such that the viscosity of a 4% aqueoussolution at 20° C. is within a range of from about 5. to about 45 MPa·s(cps), including all ranges and combination of ranges which are a subsetthereof. More preferred is a range of 11-30 MPa·s and especiallypreferred is a range of 15-25 MPa·s.

The preferred level of incorporation of itaconic acid comonomer in thevinyl alcohol-co-itaconic acid (sodium salt) copolymer, expressed as amole percentage, is within the range of from about 1.5 to about 11 mole%, including all ranges and combination of ranges which are a subsetthereof. More preferred is a range of 2.5-8.5 mole % and especiallypreferred is a range of 4-6 mole %.

The preferred degree of hydrolysis of the vinyl alcohol-co-itaconic acid(sodium salt) copolymer of the present invention, expressed as apercentage of vinyl acetate units converted to vinyl alcohol units, iswithin the range of from about 98 to 100%.

2. Copolymers with Sulfonate Functionality

Specific vinyl sulfonic acid monomers and their alkali metal salts (forexample, structure (e) below) are selected for copolymerization withvinyl acetate; the base-catalyzed alcoholysis products of thesecopolymers, which are used in the formulation of the water-soluble film,are vinyl alcohol-sulfonate salt copolymers which are rapidly soluble.

The sulfonate group may revert to sulfonic acid in the presence ofhydrogen ions but the sulfonic acid group still provides for excellentcold water solubility of the film. Examples of the selected sulfonicacid monomers (and/or their alkali metal salts) include vinyl sulfonicacid, allyl sulfonic acid, ethylene sulfonic acid,2-acrylamido-1-methylpropanesulfonic acid,2-acrylamido-2-methylpropanesufonic acid,2-methacrylamido-2-methylpropanesulfonic acid and 2-sulfoethyl acrylate.

The preferred monomer for copolymerization with vinyl acetate from thegroup of monomers providing sulphonate functionality is the sodium saltof 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and the preferredcopolymer for incorporation into the water-soluble film is therefore avinyl alcohol-co-AMPS (sodium salt) copolymer.

Copolymer Synthesis

The vinyl acetate-co-AMPS copolymer is prepared under nitrogen inmethanol as solvent, using 2,2′-azobis(isobutyronitrile) (AIBN) asinitiator. Alcoholysis of this copolymer is carried out in methanolicsodium hydroxide and the recovered vinyl alcohol-co-AMPS (sodium salt)copolymer is ground, washed to remove residual sodium acetate, anddried. These reactions are known in the art and have been reported, forexample, by Moritani and Yamauchi (Polymer, 39 (3), 553-557 (1998)).

The preferred degree of polymerization of the vinyl alcohol-co-AMPS(sodium salt) copolymer is such that the viscosity of a 4% aqueoussolution at 20° C. is in the range of from about 3 to about 18 MPa·s(cps), including all ranges and combination of ranges which are a subsetthereof. More preferred is a range of from about 4 to about 12 MPa·s.

The preferred level of incorporation of AMPS comonomer in the vinylalcohol-co-AMPS (sodium salt) copolymer, expressed as a mole percentage,is in the range of from about 1 to about 8 mole %, including all rangesand combination of ranges which are a subset thereof. More preferred isa range of from about 2.5 to about 5 mole %.

The preferred degree of hydrolysis of the vinyl alcohol-co-AMPS (sodiumsalt) copolymer, expressed as a percentage of vinyl acetate unitsconverted to vinyl alcohol units, is in the range of from about 90 toabout 99%. More preferred is a range of from about 94 to about 98%.

Water-Soluble Film Formulation-Additives

The preferred amount of the copolymer with carboxylate or sulfonatefunctionality in the water-soluble film of the present invention is inthe range of from about 40% to about 90% by weight, including all rangesand combination of ranges therein. More preferably the amount of thesecopolymers is in the range of from about 60% to about 80% by weight.

The water-soluble film of the present invention, in addition to thecopolymer with carboxylate or sulfonate functionality, may containplasticizers, lubricants, release agents, fillers, extenders,antiblocking agents, detackifying agents, antifoams and other functionalingredients. Suitable plasticizers include, but are not limited to,glycerin, diglycerin, sorbitol, ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, polyethyleneglycols up to 400 MW, neopentyl glycol, trimethylolpropane, polyetherpolyols and ethanolamines.

Preferred plasticizers are glycerin, triethyleneglycol, propylene-glycoland trimethylolpropane. The preferred amount of plasticizer incorporatedin the water-soluble film of the present invention is in the range offrom about 5% to about 30% by weight, more preferably in the range offrom about 12% to about 20% by weight.

Suitable surfactants may include the nonionic, cationic, anionic andzwitterionic classes. Preferably, the surfactants will be of thenonionic, cationic or zwitterionic classes or combinations of these.Suitable surfactants include, but are not limited to, polyoxyethylenatedpolyoxypropylene glycols, alcohol ethoxylates, alkylphenol ethoxylates,tertiary acetylenic glycols and alkanolamides (nonionics),polyoxyethylenated amines, quaternary ammonium salts and quaternizedpolyoxyethylenated amines (cationics), and amine oxides, N-alkylbetainesand sulfobetaines (zwitterionics). Preferred surfactants are alcoholethoxylates, quaternary ammonium salts and amine oxides. The preferredamount of surfactant in the water-soluble film of the present inventionis in the range of from about 0.01% to about 1% by weight, morepreferably from about 0.1% to about 0.6% by weight.

Suitable lubricants/release agents include, but are not limited to,fatty acids and their salts, fatty alcohols, fatty esters, fatty amines,fatty amine acetates and fatty amides. Preferred lubricants/releaseagents are fatty acids, fatty acid salts, and fatty amine acetates. Thepreferred amount of lubricant/release agent in the water-soluble film ofthe present invention is within the range of from about 0.02% to about1.5% by weight, more preferably from about 0.04% to about 0.15% byweight.

Suitable fillers/extenders/antiblocking agents/detackifying agentsinclude, but are not limited to, starches, modified starches,crosslinked polyvinylpyrrolidone, crosslinked cellulose,microcrystalline cellulose, silica, metallic oxides, calcium carbonate,talc and mica. Preferred materials are starches, modified starches andsilica. The preferred amount of filler/extender/antiblockingagent/detackifying agent in the water-soluble film of the presentinvention is in the range of from about 0.1% to about 25% by weight,more preferably from about 1% to about 15% by weight. In the absence ofstarch, the preferred range for a suitable filler/extender/aniblockingagent/detackifying agent is from about 1% to about 5% by weight.

Suitable antifoams include, but are not limited to, those based onpolydimethylsiloxanes and hydrocarbon blends. The preferred amount ofantifoam in the water-soluble film of the present invention is in therange of from about 0.001% to about 0.5%, and more preferably from about0.01% to about 0.1% by weight.

After formulation, the desired film thickness is within the range offrom about 5 to about 200 μm, preferably within the range of from about20 to about 100 μm, and most preferably from about 40 to about 85 μm.

Comparison Test of Film: Set-Up and Procedure

The data below represents comparative chemical compatibility testing oftwo PVOH copolymer films. The first film is a vinyl alcohol-co-itaconicacid (sodium salt) copolymer-based film representing the invention ofthe present application (Film 1), while the second film is based on ahydrolyzed vinyl acetate—methyl acrylate copolymer (Film 2).

The two films were cast with similar additives as detailed above tocreate workable film samples having the characteristics detailed inTable 1. Film thicknesses measured approximately 76 microns. Poucheshaving dimensions of approximately 7.5 cm×7.5 cm (about 3 in.×3 in.) andopen on one side were prepared using conventional heat-sealingequipment.

TABLE 1 Film Characteristics Copolymer properties: Film 1 Film 2Viscosity (cps) 20 20 Mole % comonomer 5.4 5.1 Degree of Hydrolysis(%)99.8 99.8

To each pouch was added a fill of 50 ml of Ariel Essential (Procter &Gamble, Fabric & Home Care Products—Europe), a liquid laundry detergentand the final heat seal made. While the following test specificallyreferences the packaging of a liquid laundry detergent, it should beunderstood that the present invention applies equally to the packagingof other liquid products having similar chemical incompatibilities withthe prior art films. Compatibility testing was performed over a periodof five weeks with weekly testing of film solubility in accordance withMonoSol Standard Test Method MSTM 205. Between testing periods poucheswere contained in HDPE screw-top jars at storage conditions of 38°C./80% RH. The test method is used to determine the time required for awater-soluble film to break apart (disintegrate) and its subsequentdissolution time under controlled conditions of water temperature andagitation. Before film solubility testing, the pouch was opened, theliquid detergent was discarded, and the film was cleaned by wiping withan absorbent paper towel.

The test procedure is disclosed with reference to appended FIGS. 1-3.

MONOSOL TEST METHOD 205 (MSTM 205).

Apparatus and Materials:

-   -   600 mL Beaker 12    -   Magnetic Stirrer 14 (Labline Model No. 1250 or equivalent)    -   Magnetic Stirring Rod 16 (5 cm)    -   Thermometer (0 to 100° C.,±1° C.)    -   Template, Stainless Steel (3.8 cm×3.2 cm)    -   Timer, (0-300 seconds, accurate to the nearest second)    -   Polaroid 35 mm Slide Mount 20 (or equivalent)    -   MonoSol 35 mm Slide Mount Holder 25 (or equivalent, see FIG. 1)    -   Distilled Water        Test Specimen:

-   1. Cut three test specimens from film sample using stainless steel    template (i.e., 3.8 cm×3.2 cm specimen). If cut from a film web,    specimens should be cut from areas of web evenly spaced along the    transverse direction of the web.

-   2. Lock each specimen in a separate 35 mm slide mount 20.

-   3. Fill beaker 12 with 500 mL of distilled water. Measure water    temperature with thermometer and, if necessary, heat or cool water    to maintain temperature at 20° C. (about 68° F.).

-   4. Mark height of column of water. Place magnetic stirrer 14 on base    27 of holder 25. Place beaker 12 on magnetic stirrer 14, add    magnetic stirring rod 16 to beaker 12, turn on stirrer 14, and    adjust stir speed until a vortex develops which is approximately    one-fifth the height of the water column. Mark depth of vortex.

-   5. Secure the 35 mm slide mount 20 in the alligator clamp 26 of the    MonoSol 35 mm slide mount holder 25 (FIG. 1) such that the long end    21 of the slide mount 20 is parallel to the water surface, as    illustrated in FIG. 2. The depth adjuster 28 of the holder 25 should    be set so that when dropped, the end of the clamp 26 will be 0.6 cm    below the surface of the water. One of the short sides 23 of the    slide mount 20 should be next to the side of the beaker 12 with the    other positioned directly over the center of the stirring rod 16    such that the film surface is perpendicular to the flow of the    water, as illustrated in FIG. 3.

-   6. In one motion, drop the secured slide and clamp into the water    and start the timer. Disintegration occurs when the film breaks    apart. When all visible film is released from the slide mount, raise    the slide out of the water while continuing to monitor the solution    for undissolved film fragments. Dissolution occurs when all film    fragments are no longer visible and the solution becomes clear.    Data Recording:

The results should include the following:

-   -   complete sample identification;    -   individual and average disintegration and dissolution times; and    -   water temperature at which the samples were tested.

Exposed film disintegration time (in seconds) and the time for completedissolution (in seconds) were obtained (e.g., 27 s/50 s), with theresults of the five week testing being reported in Table 2 below.

TABLE 2 Comparison Test Results Initial Solubility 1 Week 2 Weeks 3Weeks 4 Weeks 5 Weeks Film 1 27 s/50 s 23 s/53 s  31 s/86 s  44 s/129 s43 s/94 s  35 s/75 s  Film 2 33 s/58 s 56 s/117 s 67 s/152 s 75 s/192 s86 s/235 s 95 s/251 s

Solubility time increases for Film 1 are 30% for disintegration—from 27seconds to 35 seconds—and 50% for complete dissolution—from 50 secondsto 75 seconds—reflecting the conversion of one of the carboxylate groupsderiving from the itaconate moeity to a γ-lactone while the othercarboxylate group remains unaffected by hydrogen ions in the detergentformulation. In contrast, the solubility time increases for Film 2 are188% for disintegration—from 33 seconds to 95 seconds—and 333% forcomplete dissolution—from 58 seconds to 251 seconds—reflecting asubstantial conversion of the carboxylate groups present in thecopolymer of Film 2, all of which are capable of forming γ-lactones.Although complete dissolution of Film 2 eventually occurs at 10° C.,this substantial conversion of carboxylate units to lactone units isknown to have the potential to result in significant polymer residuesafter laundry wash cycles at higher temperatures.

While specific embodiments have been illustrated and described, numerousmodifications are possible without departing from the spirit of theinvention, and the scope of protection is only limited by the scope ofthe accompanying claims.

1. A water-soluble packet, comprising: (a) a copolymer film comprising ahydrolyzed copolymer which is poly(vinyl alcohol co-maleate); and (b) aquantity of liquid laundry detergent contained within the packet indirect contact with said copolymer film, said liquid laundry detergentbeing characterized by acid/base equilibria; wherein: (i) the hydrolyzedcopolymer has a degree of hydrolysis, expressed as a percentage of vinylacetate units converted to vinyl alcohol units, of about 90% to about100%; (ii) the level of incorporation of the maleate is in a range ofabout 1.5 mole % to about 11 mole %; (iii) the copolymer film, aftercontacting the liquid laundry detergent for 5 weeks, has an increase indisintegration time, measured at 10° C., expressed as a percentagerelative to the initial disintegration time, of not more than 50%; (iv)said base of the liquid laundry detergent comprises an amine; and (v)said acid of the liquid laundry detergent comprises an acid selectedfrom the group consisting of a fatty acid, an anionic surfactant acid,and combinations thereof.
 2. The water-soluble packet of claim 1,wherein the level of incorporation of the maleate is in a range of about2.5 mole % to about 8.5 mole %.
 3. The water-soluble packet of claim 1,wherein the increase in disintegration time is not more than 30%.